1. Field of the Invention
The present invention relates generally to feed-through filters arranged in power lines and signal lines to cut off noise transmitted through those lines, and more particularly to a feed-through filter, which can improve filtering performance by assigning a shielding function to a bottom surface, on which filter devices are not mounted, of the insulating substrate having a plurality of through holes into which lead terminals are respectively inserted and by improving the shielding function, and which can achieve reduction of production cost of a feed-through filter and increase the convenience in use by assigning an elastic adhesion function to the insulating substrate on which filter devices are mounted.
2. Description of the Prior Art
Generally, electromagnetic interference (EMI) is a phenomenon wherein electromagnetic waves directly radiated or conducted from electric/electronic appliances interfere with the reception of electromagnetic waves from other appliances. Alternatively, EMI also is a phenomenon wherein the reception of desired electromagnetic signals is prevented by undesirable electromagnetic signals or electromagnetic noise.
Typically, a feed-through filter is a filter in which external electrodes are grounded and conductors of internal electrodes penetrate through holes, and which cuts off noise occurring on the conductors penetrating the through holes. A feed-through capacitor mounted on the feed-through filter is problematic in that it is expensive and it is difficult to manufacture a capacitor to obtain desired capacitance when the capacitor is realized as a device for a filter. In order to solve the above problems, chip capacitors or plate capacitors, which are inexpensive and are easily mounted on a substrate, must be used. In this case, the feed-through filter can be implemented by arranging a circuit unit on an insulation resin substrate or an insulation ceramic substrate, and then mounting chip capacitors on the substrate using a surface mounting device machine. The feed-through filter implemented according to the above procedure is inserted into a metal housing or a ferrule formed in one of various shapes, thus completing the manufacturing of the feed-through filter.
In the past EMI was mainly treated within a range of electromagnetic wave noise interference. Thereafter, the handling range of EMI is extended to radiated EMI directly radiated from electric/electronic appliances, and conductive EMI conducted along power lines. With the large increase in numbers of various electronic appliances and development of digital technologies and semiconductor technologies, application fields of precision electronic appliances are widened. Therefore, EMI generated from the precision electronic appliances results in mutual malfunctioning of the precision electronic appliances, biological hazard affecting organisms such as the human body, etc., as well as electromagnetic wave noise interference. That is, the influence of electromagnetic energy on biological ecosystems is a serious issue.
Hereinafter, a conventional feed-through filter is described in detail with reference to FIGS. 1 to 3.
FIG. 1 is a perspective view of a conventional feed-through filter. Referring to FIG. 1, a ground part 11 and lead terminal connection parts 12 are formed on an insulating substrate 13 such as an alumina ceramic substrate, on which one or more lead terminal through holes 14 are formed, using a printing method. Chip capacitors 15 are disposed between the ground part 11 and the lead terminal connection parts 12, such that they are mounted on the insulating substrate 13. The construction of such a feed-through filter is disclosed in detail in U.S. Pat. No. 5,959,829.
In the conventional feed-through filter, if the insulating substrate is used as shown in FIG. 1, the lead terminal connection parts 12 and the ground part 11 surrounding the lead terminal connection parts 12 are disposed on the top surface of the insulating substrate, and the chip capacitors 16 are mounted between the lead terminal connection parts 12 and the ground part 11. However, the recent trend toward miniaturization and integration of electronic parts is rapidly spreading. Therefore, provided a filter with a narrow interval between neighboring lead terminals is produced using the conventional method of FIG. 1, it is difficult to dispose the chip capacitor between lead terminals.
FIG. 2A is a perspective view of another conventional feed-through filter and FIG. 2B is a sectional view of a conventional feed-through filter shown in FIG. 2A. Referring to FIGS. 2A and 2B, an insulator 23 through which a lead terminal 24 penetrates is disposed within an outer conductive metal ferrule 22. A chip capacitor is mounted between the lead terminal 23 and the outer conductive metal ferrule 22, and the outer conductive metal ferrule 22 is sealed with insulating resin 21. The construction of such a feed-through filter is disclosed in detail in U.S. Pat. No. 5,650,759.
However, the conventional feed-through filter of FIGS. 2A and 2B is problematic in that a shielding effect is decreased by the provision of plural lead terminals, it is difficult to manufacture the component parts of the filter, and a plurality of capacitors must be mounted by a manual operation.
FIGS. 3A to 3D are views showing the construction of a substrate for a conventional feed-through filter. Referring to FIGS. 3A to 3D, a conventional feed-through filter employs an insulating substrate 30 in which one or more lead terminal through holes 33 are formed. FIG. 3A is a top view of the insulating substrate 30, FIG. 3B is a sectional view of xcex1-xcex2 line of FIG. 3A, FIG. 3C is a bottom view of the insulating substrate 30, and FIG. 3D is an equivalent circuit diagram of the feed-through filter.
Referring to FIGS. 3A to 3D, in the conventional feed-through filter, one end electrodes C1b and C2b of chip capacitors C1 and C2 are electrically connected to lead terminal connection parts 32. Further, the other end electrodes C1a and C2a of the chip capacitors C1 and C2 are electrically connected to a top surface ground part 31. Further, a bottom surface ground part 35 is formed along the border of the bottom surface of the insulating substrate 30.
However, in the conventional feed-through filter shown in FIGS. 3A to 3D, a conductive layer is restrictedly formed only at some portion of the bottom surface of the insulating substrate 30, that is, the border of the bottom surface. Therefore, noise cannot be bypassed to the ground through the bottom surface of the insulating substrate 30 of the filter, and passes through the insulating substrate 30, so the filter cannot perform a shielding function.
As described above, in conventional feed-through filters, various methods are proposed so as to use chip capacitors, which are inexpensive and can be easily mounted, in a manufacturing process of filters. However, the conventional filters perform only a filtering function and cannot perform a shielding function through a bottom surface of an insulating substrate. That is, the conventional feed-through filters can hardly provide shielding measures.
Meanwhile, there are proposed methods of improving the shielding effect while assigning a filtering function to a feed-through filter by manufacturing metal structures and insulator structures in various shapes without using an insulating substrate. However, such methods are problematic in that they cause several difficulties, such as increase of costs, etc., due to their complicated manufacturing processes.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a feed-through filter, which can improve filtering performance by assigning a shielding function to a bottom surface, on which filter devices are not mounted, of the insulating substrate having a plurality of through holes into which lead terminals are respectively inserted, and by improving the shielding function.
Another object of the present invention is to provide a feed-through filter, which can intercept the transmission of noise due to unstable mounted states, that is, a gap between a mounting surface of a casing and the feed-through filter can maintain and improve adherence of the filter to the casing by application of conductive silicon in the shape of a band to the top surface of the insulating substrate, which is a mounting surface, or a bottom surface thereof, when the feed-through filter is mounted in the metal casing or metal housing.
A further object of the present invention is to provide a feed-through filter, which can achieve the reduction of production cost and increase the convenience of use, such as ease of mounting, by assigning an elastic adhesion function to an insulating substrate on which filter devices are mounted.
In order to accomplish the above object, the present invention provides a feed-through filter having an improved shielding function, comprising an insulating substrate having top, bottom and side surfaces; one or more lead terminal through holes passing through the top and bottom surfaces of the insulating substrate; one or more lead terminal connection parts separately formed around the through holes on the top surface using conductive materials, and electrically connected to the lead terminals inserted into the through holes to pass therethrough; a top surface ground part formed along the border of the top surface of the insulating substrate in the shape of a band using conductive material, and formed to be spaced apart from the lead terminal connection parts; one or more filter devices each having a first electrode electrically connected to the lead terminal connection parts and a second electrode electrically connected to the top surface ground part; and a bottom surface ground part electrically separated from the lead terminals by non-conductive regions, which are formed around the lead terminals inserted into the lead terminal through holes in shapes of doughnuts, on the bottom surface of the insulating substrate, and made of conductive material.
In the present invention, the bottom surface ground part is formed on the bottom surface of the insulating substrate so as to provide a noise shielding function to the insulating substrate of the feed-through filter, wherein the bottom surface ground part is formed on the bottom surface of the insulating substrate in a specific pattern using a conductive material. For example, the bottom surface ground part can be formed in a mesh pattern using a conductive material. Alternatively, the bottom surface ground part can be formed of a conductive material on the entire bottom surface of the insulating substrate.
Further, the present invention provides a ground connection means for electrically connecting the top and bottom surface ground parts to each other so as to increase the shielding effect of the feed-through filter of the present invention. The ground connection means comprises one or more fine conductive via holes formed to pass through the top and bottom surfaces of the insulating substrate, thus enabling the top surface ground part and the bottom surface ground part to be electrically connected to each other through the conductive via holes. Alternatively, one or more conductive side surface connection parts are formed on side surfaces of the insulating substrate, wherein the top and bottom surface connection parts are electrically connected to each other through the side surface connection parts.
Further, in the present invention, conductive silicon for intercepting the transmission of noise by eliminating gaps between the substrate for a filter and a metal casing is formed on the top and bottom surfaces of the insulating substrate so as to achieve close adhesion of the feed-through filter of the present invention.
Further, in the present invention, an additional conductive shielding substrate can be attached to the bottom surface of the insulating substrate so as to provide a noise shielding function to the insulating substrate of the feed-through filter of the present invention.
Further, in the present invention, a flexible substrate can be used as the insulating substrate of the feed-through filter so as to achieve simple mountability of the feed-through filter, a plurality of through hole slits are formed at predetermined intervals along the internal surface of each of the through holes, and a plurality of substrate slits are formed at predetermined intervals along the border of the insulating substrate.